The present invention relates to positioners for positioning objects, and more particularly to a deformable positioning stage.
Assembly of optic-electronic devices requires precision alignment of optical fibers with lasers or sensors and then bonding. A worker looking through a microscope at the end of a fiber conventionally executes this precision alignment and bonding process.
The alignment and bonding process can take as little as five minutes. However, if there is a misalignment of the fiber ends, this process can take as long as forty-five minutes to an hour. Misalignment often occurs because the fibers are subject to other than pure linear movement during the alignment process. Accordingly, a need exists for an improved alignment process which will reduce, if not eliminate, misalignment of a fiber end.
It is likely that in the next ten years the use of opto-electronic devices will spread to automobiles and every phone and computer manufactured in the United States, resulting in an estimated volume of 25 million units produced per year. Conventional assembly of opto-electronic devices can, as discussed above, require substantial worker time and therefore be quite costly. Accordingly, a need exists for a way to assemble opto-electronic devices which would require less worker effort and hence reduce the cost of assembly.
In other fields, delicate precision micrometer, sub-micrometer and nanometer assembly or positioning is also required. Such fields include medicine, biotechnology and electronic manufacturing. For example, individual atoms, molecules or nano-particles may be combined or separated to build materials and devices exhibiting desirable properties. Positioning devices currently available do not provide the precision and range of motion required in these and other technological fields. Accordingly, an improved technique is required for performing precision movement, often referred to as fine movement, at each of the micrometer, sub-micrometer and nanometer levels.
A planar biaxial micropositioning stage, which includes a deformable structure micro-positioning stage and which utilizes two nested cantilever flexure mechanisms facilitating movement of the stage in each of the X and Y axes has been proposed for use in precision manufacturing. A force can be applied to the proposed structure by an actuator to move the stage along the intended axis of movement. The actuator placement in this positioner is perpendicular to the axis of movement of the stage. However, the resulting movement in each of the X and Y directions is not purely linear. Rather, the proposed structure introduces a yaw which is unacceptable for precision manufacturing applications. This yaw is often referred to as a rotational cross talk error.
Known prior art positioning devices cannot eliminate rotational cross talk unless additional actuators are included in the device to apply counterbalancing rotation and thereby ensure pure linear movement. These actuators add undesirable complexity and costs to the devices. Additionally, complex control algorithms must be developed and used to operate multiple actuators in concert to compensate for the cross talk.
In the proposed micro-positioning stage discussed above, as well as other proposed stages, the rotational cross talk error is inherent in the design. That is, applying a force intended to move a stage in one direction necessarily produces an unintended rotation. Accordingly, a need exists for a micro-positioner which does not impart rotational cross talk error into intended linear movement.
Control of conventional micro-positioners is performed through the use of feedback loops. At least one sensor is required to measure movement of a stage. Conventional deformable structure micro-positioners use sensors which are typically located at a position which results in inaccurate measurement of the true stage displacement. This inaccuracy due to sensor placement is commonly referred to as Abbe effect. Accordingly, a positioner is required which provides more accurate sensing.
Conventional deformable structure micro-positioners require that the actuator used to impart a force upon a movable stage be attached to the movable stage with an epoxy compound, or some other adhesive. These attachments impart a loss of force into the system. For example, when a force is applied to an epoxy connection between the actuator and the moving stage, the epoxy compresses, resulting in up to a 60 percent loss in applied force. Hence, an improved technique is required to attach an actuator to a movable stage to reduce the loss of force.
Using an epoxy or screws for the coupling, it is also difficult to obtain a pure parallel alignment of the actuator and the moving stage. Unparallel alignment results in a loss of force in the system. Furthermore, misalignment between the components may produce damaging stresses on the actuator. Accordingly, an improved coupling is required to achieve a parallel attachment between the coupling and an actuator.
Epoxy couplings are also subject to maintenance difficulties and durability limits. To remove an actuator from a deformable structure micro-positioner with epoxy couplings, the epoxy coupling must be cut using a machine tool. The two surfaces exposed by the cutting must be cleaned before they are reattached. This cutting and cleaning process may damage both the actuator and the deformable structure micro-positioner. Accordingly, a need exists for an improved technique of attaching and removing an actuator from a micro-positioner which eliminates the potentially damaging cutting and cleaning process.
Conventional deformable structure micro-positioners can be subjected to forces which may damage the individual components of a positioner. These forces may include inadvertent contact with the movable stage portion of the positioner or over-actuation of a drive used to move the movable stage. Accordingly, a need exists for a deformable structure micro-positioner which can better withstand damaging forces.
Deformable structure micro-positioners with one and two-degrees of freedom are well known. Six-degree of freedom positioners in the macro-scale are common. One type of six-degree of freedom positioner is often referred to as a Stewart platform. One familiar use of Stewart platforms is in aircraft simulators. However, a practical adaptation of macro-scale Stewart platforms to the micro-scale using a deformable structure platform has not been previously achieved.
A Stewart platform utilizes six struts to support a platform. Historically, macro-scale Stewart platform devices place drives, e.g. actuators, in each of the struts to obtain movement of the platform. In the proposed micro-scale adaptations of Stewart platforms, actuators are also placed in the struts. However, actuators of the type typically used in micro-scale positioners do not have the required range of motion necessary for use in the struts of a micro-scale adapted Stewart platform. Hence, more expensive and much larger actuators must be used in the proposed micro-scale Stewart platforms.
The February 1994 issue of NASA Tech Briefs proposed a positioner, characterized as a minimanipulator, with six-degrees of freedom. The drives which produce movement of the platform include stepping motors and rotary actuators. Each of these drives is subject to sticktion and backlash. Hence, this manipulator is not capable of achieving fine movement, since none of the actuator configurations usable in this device can produce movement without some sticktion and/or backlash. Accordingly, a need exists for an improved six-degree of freedom positioner which is capable of providing fine movement in each of the six degrees of freedom.
The conventional process for manufacturing deformable structure micro-positioning devices is costly and time-consuming. Typically, each device must be individually machined from a separate piece of material. Additionally, six-degree of freedom micro-positioners require separate manufacturing and assembly steps for each of the individual positioners. Accordingly, a need exists for a manufacturing process to produce a plurality of deformable structure micro-positioning devices, including six-degree of freedom devices, which is less costly and time-consuming.
One object of the present invention is to provide an improved technique for fine precision object manipulation in manufacturing and assembly processes.
Another object of the present invention is to provide a micro-positioning stage with precision movement on at least one of the micrometer, sub-micrometer and nanometer levels.
Another object of the present invention is to provide a micro-positioning stage with pure translational or rotational movement along an intended axis of movement.
Another object of the present invention is to provide a micro-positioning stage which is less susceptible to permanent deformation due to the application of an excessive force.
Another object of the present invention is to provide an improved technique for manufacturing one-, two-, three-, four-, and six-degree of freedom micro-positioners.
Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from this disclosure, including the following detailed description, as well as by practice of the invention. While the invention is described below with reference to preferred embodiment(s), it should be understood that the invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the invention as disclosed and claimed herein and with respect to which the invention could be of significant utility.
In accordance with the present invention, a positioning device is provided. The positioning device may be used to position many different types and sizes of objects. These objects can range from large objects, which are often referred to as macro-scale objects, to very small objects, commonly referred to as micro-scale objects. Objects in the micro-scale are measured in micrometers. Even smaller objects in the micro-scale are measured in sub-micrometers. And, extremely small objects in the micro-scale are measured in nanometers. Objects at the nano-level are smaller than those measured in sub-microns. Objects in this smallest scale can include individual atoms.
The positioning device of the present invention includes a movable stage. The movable stage is where objects to be positioned are placed for positioning. The movable stage has two perpendicular axes, which will be referred to as a Y-axis and an X-axis. The axes preferably intersect at the center of the movable stage. In this preferred configuration, each axis divides the movable stage into two halves.
In a first embodiment of the present invention, the positioning device also includes two levers for moving the movable stage. Together, the two levers form a pair of levers. Each of the pair of levers is positioned so as to be parallel to, for example, the X-axis. In this case, one lever of the pair of levers is positioned on one side of the Y-axis, and the other lever is positioned on the other side of the Y-axis, with each lever being the same distance away from the Y-axis. Hence, the first and second levers are mirror images of one another and positioned symmetric about the Y-axis. Each of the levers applies a force to the movable stage to move the movable stage.
In a second embodiment of the present invention, a second pair of levers may also be included in the positioning device if so desired. The second pair of levers is preferably a mirror image of the first pair of levers and positioned symmetric about the X-axis. Thus, each of the second pair of levers is positioned the same distance from the X-axis as the first pair of levers, but on the other side of the X-axis. Furthermore, each of the second pair of levers are placed the same distance from, but on opposite sides of, the Y-axis.
Advantageously, each of the levers, whether two, four or some other number of levers is utilized, is attached to both the movable stage and a support member. Each attachment forms a pivot. Each lever thus pivots about its attachment to the movable stage and its attachment to the support structure. The pivot attachments are preferably designed to bend, and are referred to as flexures.
Like the levers, the flexures are positioned in a mirrored configuration about the X and/or Y axes. If two pairs of levers are provided, the flexure attaching one lever of the first pair of levers and the flexure attaching one lever of the second pair of levers to the movable stage are positioned the same distance from, but on opposite sides of, the X-axis. The flexures attaching the other levers of the first and second pairs of levers to the movable stage are also positioned the same distance from, but on opposite sides of, the X-axis. Also, the flexures attaching the one levers of the first and second pairs of levers and the flexures attaching the other levers of the first and second pairs of levers to the movable stage are positioned the same distance from, but on opposite sides of, the Y-axis.
Likewise, the flexure attaching one lever of the first pair of levers and the flexure attaching one lever of the second pair of levers to the support member are positioned the same distance from, but on opposite sides of, the X-axis. The flexures attaching the other levers of the first and second pairs of levers to the support member are also positioned the same distance from, but on opposite sides of, the X-axis. Also, the flexures attaching the one levers of the first and second pairs of levers and the other levers of the first and second pairs of levers to the support member are positioned the same distance from, but on opposite sides of, the Y-axis.
In accordance with still another aspect of the invention, the support member, the movable stage, the first and the second pairs of levers, and each of the eight flexures form a single unit. That is, the components are monolithic and formed out of a single piece of material, thus being inseparable.
Advantageously, each lever includes a cantilever. The cantilever serving to modify the magnitude of a force exerted on one end of a lever and applied by the other end. Accordingly, the input force to a lever can be different than the output force from the lever.
Preferably, the positioning device includes at least one member which prevents the movable stage from moving beyond a predetermined distance. This member, referred to as a stop member, can be formed in or attached to either the movable stage or the support member. For example, a slot, or hole, can beneficially be formed into the movable stage, and a rod, or some other type member, is placed into the slot. The slot is formed such that when a rod is placed into the slot, a portion of the rod extends into a gap between the movable stage and one of the levers. When the movable stage moves to a certain position, the rod comes in contact with the applicable lever, thereby beneficially preventing the stage from moving beyond a predetermined distance. For stop members formed in the support member, the configuration can be much the same, except that the slot is formed into the support member. The rod extends into a gap between a lever and the support member. As the movable stage and lever move, the lever comes in contact with the rod when the stage moves to a certain position.
In accordance with a third embodiment of the present invention, yet another pair of levers is included to move the movable stage. This pair is positioned parallel to the Y-axis and is also a mirrored pair of levers. Each of the levers is positioned equi-distance from, but on opposite sides of, the X-axis.
Yet another pair of levers positioned parallel to the Y-axis of the movable stage, but on the opposite side of the Y-axis than the first pair of Y-axis levers, can, if desired, also be included in the positioning device. This lever pair too is in a mirror configuration. Each of this pair of levers is positioned an equal distance from, but on opposite sides of, the X-axis. The two pairs of levers positioned parallel to the Y-axis are also positioned an equal distance from, but on opposite sides of, the Y-axis of the movable stage.
In yet another aspect of the invention, each of the levers may include a nested lever member. That is, each lever may have at least two lever members. The nested lever members are positioned such that one of the nested lever members is closer to the moving stage than another of the nested lever members. Thus, the combined length of the nested lever members is less than the length of the single lever which would otherwise be required.
According to other aspects of the invention, each of the levers is moved in an arc to move the positioning stage. In moving a pair of levers, the arcs are mirror images of one another about an axis, e.g. a Z-axis, of the positioning stage. Furthermore, the directions in which the levers are moved along the respective arcs are opposed directions.
According to still other aspects of the invention, the components of a positioning stage are machined into a solid material such as a solid block of aluminum, or other monolithic material. The machining may be electric discharge machining, or some other machining process. Each of the components is preferably machined into the material at the same angle. In such a case, the machined material is then sliced at a second angle into several slices.
Beneficially, the second angle is perpendicular to the first angle and each slice is identical to the other slices. Each of these slices thereby forms a single positioning stage. However, if desired, more than one positioning stage can be machined into the monolithic material at the first angle. Thus, when sliced, each slice may contain more than one positioning stage.